Cthrc1 lowers pulmonary collagen associated with bleomycin-induced fibrosis and protects lung function

Idiopathic pulmonary fibrosis (IPF) involves collagen deposition that results in a progressive decline in lung function. This process involves activation of Smad2/3 by transforming growth factor (TGF)-β and Wnt signaling pathways. Collagen Triple Helix Repeat-Containing-1 (Cthrc1) protein inhibits Smad2/3 activation. To test the hypothesis that Cthrc1 limits collagen deposition and the decline of lung function, Cthrc1 knockout (Cthrc1^-/-) and wild-type mice (WT) received intratracheal injections of 2.5 U/kg bleomycin or saline. Lungs were harvested after 14 days and Bronchoalveolar lavage (BAL) TGF-β, IL1-β, hydroxyproline and lung compliance were assessed. TGF-β was significantly higher in Cthrc1^-/- compared to WT (53.45 ± 6.15 ng/mL vs. 34.48 ± 11.05) after saline injection. Bleomycin injection increased TGF-β in both Cthrc1^-/- (66.37 ± 8.54 ng/mL) and WT (63.64 ± 8.09 ng/mL). Hydroxyproline was significantly higher in Cthrc1^-/- compared to WT after bleomycin-injection (2.676 ± 0.527 μg/mg vs. 1.889 ± 0.520, P = 0.028). Immunohistochemistry of Cthrc1^-/- lung sections showed intracellular localization and activation of β-catenin Y654 in areas of tissue remodeling that was not evident in WT Lung compliance was significantly reduced by bleomycin in Cthrc1^-/- but there was no effect in WT animals. These data suggest Cthrc1 reduces fibrotic tissue formation in bleomycin-induced lung fibrosis and the effect is potent enough to limit the decline in lung function. We conclude that Cthrc1 plays a protective role, limiting collagen deposition and could form the basis of a novel therapy for pulmonary fibrosis.